The present invention relates to a vinylidene chloride polymer composition, and films made from the composition, including films suitable for the packaging of food products, such as meat.
Thermoplastic packaging films made of vinylidene chloride polymer (herein referred to as xe2x80x9cPVdCxe2x80x9d), have been used for the packaging of food products such as fresh and processed meats and other items.
Multilayer, oriented, heat-shrinkable films including at least one layer containing PVdC have been produced by extrusion, coextrusion, lamination, and extrusion coating.
Chinese sausage is currently packaged in films such as monolayer films made up of a DOW 2032(trademark) PVdC and formulated with plasticizers, heat stabilizers, antioxidants, UV absorbers, pigments, slip agents, antiblock agents, etc. Although this film offers good package color and thermal stability during extrusion of the packaging film, it exhibits a marginally stable trapped bubble, and a very narrow processing window, during orientation. As a result, manufacture of the film becomes a very difficult process in which bubble instability during orientation can easily occur. This can and does result in downtime from failure of the trapped bubble, or in processing speeds that are slower (and hence more expensive) than desirable to avoid such bubble failure.
An alternative PVdC copolymer, POVIDEN(trademark) Type 2 PVdC having a weight average molecular weight of 130,000, and available from Kaustic of Volgograd, Russia, was tested by the applicant by extruding this material into a monolayer film and orienting the film. This was an effort to identify and provide a material which helps provide a more stable bubble process. However, it was found that although a more stable bubble process was obtained, this was at the expense of greater thermal instability during extrusion, leading to a film with too dark a color.
The applicant has now discovered that the composition disclosed herein, provides a combination of good thermal stability, color appearance, extrudability, orientability, Young""s modulus, package firmness, and free shrink ratio properties in films of the invention, that is unavailable from either the DOW 2032 vinylidene chloride polymer alone, or the POVIDEN vinylidene chloride polymer alone.
A composition comprises greater than 50% by weight of a first vinylidene chloride polymer having a weight average molecular weight of between 80,000 and 125,000, and less than 50% by weight of a second vinylidene chloride polymer having a weight average molecular weight of between 126,000 and 180,000, the weight percent of each of the first and second polymers based on the combined weight of the first and second polymers.
A composition comprises between 51% and 99% by weight of a first vinylidene chloride polymer having a weight average molecular weight of between 80,000 and 125,000, and between 1% and 49% by weight of a second vinylidene chloride polymer having a weight average molecular weight of between 126,000 and 180,000, the weight percent of each of the first and second polymers based on the combined weight of the first and second polymers.
A film comprises at least one layer comprising a composition having greater than 50% by weight of a first vinylidene chloride polymer having a weight average molecular weight of between 80,000 and 125,000, and less than 50% by weight of a second vinylidene chloride polymer having a weight average molecular weight of between 126,000 and 180,000, the weight percent of each of the first and second polymers based on the combined weight of the first and second polymers.
A film comprises at least one layer comprising a composition having between 51% and 99% by weight of a first vinylidene chloride polymer having a weight average molecular weight of between 80,000 and 125,000, and between 1% and 49% by weight of a second vinylidene chloride polymer having a weight average molecular weight of between 126,000 and 180,000, the weight percent of each of the first and second polymers based on the combined weight of the first and second polymers.
A biaxially oriented film comprises at least one layer comprising a blend of a first vinylidene chloride polymer and a second vinylidene chloride polymer, the film having a free shrink ratio of between 0.6 and 2.2 at a shrink temperature of 180xc2x0 F.
A biaxially oriented film comprises at least one layer comprising a blend of a first vinylidene chloride polymer and a second vinylidene chloride polymer, the film having a free shrink ratio of between 0.8 and 1.4 at a shrink temperature of 200xc2x0 F.
Definitions
xe2x80x9cvinylidene chloride polymerxe2x80x9d and xe2x80x9cPVdCxe2x80x9d herein refer to a vinylidene chloride-containing polymer or copolymer, i.e., a polymer that includes monomer units derived from vinylidene chloride (CH2=CCl2) and also, optionally, monomer units derived from one or more of vinyl chloride, styrene, vinyl acetate, acrylonitrile, and C1-C12 alkyl esters of (meth)acrylic acid (e.g., methyl acrylate, butyl acrylate, methyl methacrylate, etc.). Thus, xe2x80x9cvinylidene chloride polymerxe2x80x9d and xe2x80x9cPVdCxe2x80x9d include one or more of vinylidene chloride homopolymer, vinylidene chloride/vinyl chloride copolymer, vinylidene chloride/methyl acrylate copolymer, vinylidene chloride/acrylonitrile copolymer, vinylidene chloride/butyl acrylate copolymer, vinylidene chloride/styrene copolymer, and vinylidene chloride/vinyl acetate copolymer. The weight percent of the vinylidene chloride monomer can be between 75% and 95% by weight of the copolymer; the weight percent of the second monomer, e.g. vinyl chloride, can be between 5% and 25% by weight of the copolymer;
xe2x80x9c(meth)acrylic acidxe2x80x9d herein refers to both acrylic acid and/or methacrylic acid;
xe2x80x9c(meth)acrylatexe2x80x9d herein refers to both acrylate and methacrylate;
xe2x80x9cpolymerxe2x80x9d herein refers to the product of a polymerization reaction, and is inclusive of homopolymers, copolymers, terpolymers, tetrapolymers, etc.;
xe2x80x9ccopolymerxe2x80x9d herein refers to a polymer formed by the polymerization reaction of at least two different monomers and is inclusive of random copolymers, block copolymers, graft copolymers, etc.;
xe2x80x9cethylene/alpha-olefin copolymerxe2x80x9d (EAO) herein refers to copolymers of ethylene with one or more comonomers selected from C3 to C10 alpha-olefins such as propene, butene-1, hexene-1, octene-1, etc. in which the molecules of the copolymers comprise long polymer chains with relatively few side chain branches arising from the alpha-olefin which was reacted with ethylene. This molecular structure is to be contrasted with conventional high pressure low or medium density polyethylenes which are highly branched with respect to EAOs and which high pressure polyethylenes contain both long chain and short chain branches. EAO includes such heterogeneous materials as linear medium density polyethylene (LMDPE), linear low density polyethylene (LLDPE), and very low and ultra low density polyethylene (VLDPE and ULDPE), such as DOWLEX(trademark) or ATTANE(trademark) resins supplied by Dow, ESCORENE(trademark) or EXCEED(trademark) resins supplied by Exxon; as well as linear homogeneous ethylene/alpha olefin copolymers (HEAO) such as TAFMER(trademark) resins supplied by Mitsui Petrochemical Corporation, EXACT(trademark) resins supplied by Exxon, or long chain branched (HEAO) AFFINITY(trademark) resins supplied by the Dow Chemical Company, or ENGAGE(trademark) resins supplied by DuPont Dow Elastomers;
xe2x80x9cpackagexe2x80x9d herein refers to a film configured around a product;
xe2x80x9cfilmxe2x80x9d herein refers to plastic web materials having a thickness of 0.50 mm (20 mils) or less such as 0.25 mm (10 mils) or less;
xe2x80x9cinner layerxe2x80x9d herein refers to any layer of a multilayer film having both of its principal surfaces directly adhered to another layer of the film;
xe2x80x9couter layerxe2x80x9d herein refers to any layer of a film having only one of its principal surfaces directly adhered to another layer of the film;
xe2x80x9cseal layerxe2x80x9d herein refers to a layer of a film that can be involved in the sealing of the film to itself or another layer;
xe2x80x9csealxe2x80x9d herein refers to a bonding of a first film surface to a second film surface created by heating (e.g., by means of a heated bar, hot air, infrared radiation, ultrasonic sealing, etc.) the respective surfaces to at least their respective seal initiation temperatures;
xe2x80x9cbarrierxe2x80x9d herein refers to a layer of a film that can significantly retard the transmission of one or more gases (e.g., O2);
xe2x80x9cabuse layerxe2x80x9d herein refers to a layer of a film that can resist abrasion, puncture, and/or other potential causes of reduction of package integrity, and/or potential causes of reduction of package appearance quality;
xe2x80x9ctie layerxe2x80x9d herein refers to a layer of a film that can provide interlayer adhesion to adjacent layers that include otherwise nonadhering or weakly adhering polymers;
xe2x80x9cbulk layerxe2x80x9d herein refers to a layer of a film that can increase the abuse resistance, toughness, or modulus of a film;
xe2x80x9claminationxe2x80x9d herein refers to the bonding of two or more film layers to each other, e.g. by the use of polyurethane adhesive;
xe2x80x9ctotal free shrinkxe2x80x9d means the percent dimensional change in a 10 cmxc3x9710 cm specimen of film, when shrunk at a specified test temperature such as 85xc2x0 C. (185xc2x0 F.), with the quantitative determination being carried out according to ASTM D 2732, as set forth in the 1990 Annual Book of ASTM Standards, vol. 08.02, 368-371, the entire disclosure of which is incorporated herein by reference. xe2x80x9cTotal free shrinkxe2x80x9d refers to the totality of the free shrink in both the longitudinal direction and the transverse direction.
xe2x80x9cfree shrink ratioxe2x80x9d is the ratio of the free shrink of a given film, at a given temperature, in the longitudinal direction, to the free shrink of the same film, at the same temperature, in the transverse direction;
xe2x80x9cmachine directionxe2x80x9d herein refers to the direction along the length of a film, i.e., in the direction of the film as it is formed during extrusion and/or coating; and
xe2x80x9ctransverse directionxe2x80x9d herein refers to the direction across a film, i.e., the direction that is perpendicular to the machine direction.
All compositional percentages used herein are presented on a xe2x80x9cby weightxe2x80x9d basis, unless designated otherwise.